Synthesis of 4-Aryl Pyrrolo[1,2-α]quinoxalines via Iron-Catalyzed Oxidative Coupling from an Unactivated Methyl Arene

J Org Chem. 2021 Jun 4;86(11):7390-7402. doi: 10.1021/acs.joc.1c00371. Epub 2021 May 24.

Abstract

Herein, we describe the direct synthesis of pyrrolo[1,2-α]quinoxaline via oxidative coupling between methyl arene and 1-(2-aminophenyl) pyrroles. Oxidation of the benzylic carbon of the methyl arene was achieved by di-t-butyl peroxide in the presence of an iron catalyst, followed by conversion to an activated aldehyde in situ. Oxygen played a crucial role in the oxidation process to accelerate benzaldehyde formation. Subsequent Pictet-Spengler-type annulation completed the quinoxaline structure. The protocol tolerated various kinds of functional groups and provided 22 4-aryl pyrrolo[1,2-α]quinoxalines when various methyl arene derivatives were used. The developed method proceeded in air, and all catalysts, reagents, and solvents were easily accessible.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Catalysis
  • Iron*
  • Molecular Structure
  • Oxidative Coupling
  • Quinoxalines*

Substances

  • Quinoxalines
  • Iron